1. Field of the Invention
The present invention relates to a lancer for withdrawing a sample of blood from a patient via a lancet. More particularly, the invention is drawn to a lancer having a latch triggering mechanism for actuating the device. The lancer optionally has an adjustable tip for setting the depth of penetration of the lancet into the patient's skin by moving a lancet stop back and forth. The lancer may further include an ejection mechanism for automatically causing the release of the lancet from the lancer without the need to handle the lancet. Moreover, the lancer may include a dampening mechanism, such as a wisp, for reducing vibrations in the lancet, thus increasing patient comfort. The lancet may further include a centering mechanism to decrease undesired motions of the lancet perpendicular to the axial direction, when the lancet is fired.
2. Brief Description of the Art
Ballistic-type lancers are commonly used devices in the medical field for making a small puncture in a patient's skin to obtain a blood sample. One such lancer comprises a hollow lancer body and a lancet containing a sharpened needle, also known as a stylet. The lancet is mounted by the user onto a plunger within the lancer body. The plunger is capable of moving axially (back and forth) within the lancer body. The plunger is surrounded by a coil spring, which becomes compressed when the plunger is pulled back or “armed” by the user. The plunger is held in place by a trigger with the compressed spring exerting a force against the plunger. The lancer is now said to be in an armed state. The armed lancer is grasped by the user and its bottom is pressed against the patient's skin. When the plunger is released by the user by actuating the trigger, the spring decompresses, driving the plunger, and the attached lancet, toward the bottom of the lancer. As the propelled lancet hits a stop at the bottom of the lancer, its projecting stylet is pushed through a hole in the stop, which in turn swiftly pierces the patient's skin so that a drop of blood can be removed therefrom. That drop of blood may then be used for testing, such as blood glucose testing for diabetics. This lancer, however, does not completely meet the needs of patients and other users, such as medical personnel who employ the lancers to obtain samples from patients, for reasons described below.
To hold the plunger in the armed state, the conventional lancer, described above, uses a pawl-like trigger integrally attached to the bottom end of the plunger. When the plunger is cocked, the tip of the pawl-like trigger is received into an opening in the lancer body, thereby holding the spring-loaded plunger in place. A small button is positioned over the lancer body opening to allow the user to actuate the trigger, i.e., push the pawl tip out of the receiving hole and back into the lancer body. This pawl-like or detent-based trigger, however, can be actuated with relatively little force, which may result in an inadvertent firing of the lancet and the accidental piercing of the patient's or user's skin. Therefore, an improved triggering mechanism is desired that reduces the likelihood of accidental firing by actuating only when sufficient and intended pressure is applied thereto.
Also, because the pawl-like trigger is integral to the plunger, it places a bias force on the plunger. That bias force, however, is not in the same direction of the spring force on the plunger, and may adversely affect the operation of the plunger by causing it to deviate from its axial path of motion. This in turn can reduce patient comfort upon penetration of the stylet. Consequently, it is also desired that the improved triggering mechanism minimize introduction the of non-axial motion to the plunger so that it can have a more linear path of motion, thus increasing patient comfort.
The penetration depth of the stylet into the patient's skin is another important consideration in patient comfort, as well as being a major factor in determining the amount of blood that will be obtained from the patient (stylet gauge being the other major factor). Generally, as the stylet penetration depth increases, the amount of blood increases, as well as the patient discomfort. However, the required depth of penetration will differ from patient to patient, because skin thickness varies depending on the patient's age, gender, the extent to which it has been previously lanced, and other factors. If the penetration depth is set by the lancer design to be too shallow for the specific patient, the stylet may not adequately pierce the patient's skin, and repeated lancing attempts or smaller gauge (larger diameter) stylets may be required to extract the required amount of blood, which in turn wastes time and/or lancets, and in any event increases patient discomfort. On the other hand, if the lancer is designed to cause the stylet to penetrate too deeply for a specific patient, unnecessary discomfort will be incurred by that patient, as well as a longer recovery time.
A certain conventional lancer has been designed to have an adjustable stylet firing depth, wherein the distance that the plunger moves is precisely controlled to achieve the desired penetration depth of the stylet. However, to achieve this precise plunger control, complicated drive mechanisms involving many low tolerance and expensive components are required, as well as time-consuming and labor-intensive assembly.
Other conventional lancers allow for imprecise plunger movement, but instead accommodate cap (or tip) assemblies to permit the patient or other user to set for himself or herself a desired stylet penetration depth. The bottom of the cap assembly stops the movement of the lancet, and the stylet passes through a hole in the bottom of the cap to pierce the skin. For example, one type of lancer is designed to receive interchangeable caps. Each cap has, at its bottom, an annular stop portion, to stop the lancet. The lancet stop surrounds the hole that lets the stylet pass through. The bottom of the cap assemblies are each made to have a different thickness. Thicker bottoms provide a shallower stylet penetration depth, and thinner bottoms provide a deeper stylet penetration depth. The user selects the desired depth of penetration by placing one of the set of interchangeable caps onto the lancer. This adjustment technique, however, requires the manufacture, stocking and purchase of many various cap assemblies of differing thickness.
Another type of depth penetration adjusting assembly works by placing the lancet stop portion within the assembly itself. The bottom (distal) portion of the assembly has a hole that corresponds to the hole within the lancet stop, and the stylet passes through both the lancet and bottom holes. In this type of adjustable cap, the bottom of the cap is caused to move back and forth to provide respectively a smaller or larger space between the lancet stop and the bottom of the cap, which in turn respectively increases and decreases the stylet penetration depth.
One such depth penetration adjustment assembly includes three elements. The first is a cap element having its near end coupled to the lancer. At the distal end of the cap element is the lancet stop and an opening through which the stylet passes. The assembly secondly includes a cover element forming its bottom. The cover element also has an opening through which the stylet passes that corresponds to the opening in the cap element. The assembly has a third adjusting element disposed between, and engaging, the cap and cover elements. The adjusting element has a recessed portion on its outside to engage the cover element, which permits the adjusting element to rotate with the cover element when engaged. The adjusting element/cover element subassembly are engaged to the cap element via a threaded fitting, which allows the adjusting element/cover element subassembly to turn like a screw with respect to the cap element, which translates into axial movement of the bottom of the cover element with respect to the lancet stop of the cap element. This causes a variation of the stylet penetration depth. However, this device requires the manufacture and assembly of three discrete elements. Moreover, because the bottom cover element moves to achieve a variation in depth, the overall length of the lancer will vary depending on the adjustment setting, inhibiting easy storage and use of the lancer. Also, the depth setting can change since the tip may be rotated while being assembled on the device.
Another conventional depth penetration adjustable cap assembly also uses three elements: an inner sleeve having the lancet stop, an intermediate ring having a first helical incline camming surface, and an outer sleeve, having the bottom opening and a second helical incline camming surface. This assembly is likewise coupled to the lancer. The camming surfaces of the combined assembly capture a cam on the inner sleeve. When the outer sleeve is rotated, the cam forces the outer sleeve to move away from the lancer, thus increasing the distance between the lancet stop and the bottom of the outer sleeve, which in turn decreases the depth penetration. This assembly, however, suffers from the same problems as the previously described one.
Although all of the above-described adjustable depth penetration assemblies regulate the amount of skin penetration, and to a certain extent allow for easy adjustment, it is desired to have one that minimizes resetting errors when removing and replacing the cap.
In another aspect of conventional lancer operation, after the lancet has been used to draw blood from a patient it becomes contaminated with blood and, thus, poses a potential health hazard to anyone else who might be stuck by its stylet. Conventional lancers with ejection capabilities typically utilize a control member that is held by an operator. Unfortunately, if the operator removes a finger from the control member prior to complete separation, an accidental lancet ejection can result. In an attempt to prevent this, one conventional type of ejection mechanism utilizes a retention recess that retains the control member to permit ejection. This solution is less than optimal since there is still a possibility of accidental ejection. Other known ejection mechanisms tend to be cumbersome and require complicated manipulations, which are difficult for blind or disabled diabetics to accomplish, and increase the likelihood of accidental needle stick injury. In order to overcome the problems associated with the known lancet ejection mechanisms, it is desirable for the lancer to be capable of easily and automatically ejecting the contaminated lancet with the patient or other user using motions already known or familiar to the user.
In another aspect of conventional lancers, the spring-loaded plunger/lancet assembly may produce vibrations upon it being fired. In particular, the release of the compressed spring exerts a force on a plunger/lancet assembly to accelerate the same. The lancer's system dynamics, due primarily to the main spring that accelerates the plunger, are such that the plunger may vibrate in the axial direction after the lancet has rebounded from its stopping component. These vibrations may thus reduce the optimum propulsion of the lancet and reduce the comfort of the patient, because even small vibrations can be sensed by the patient upon lancing of the skin. It thus would be desirable to provide a lancer having a mechanism for dampening these vibrations and frictional dampening of axial movement, and thereby increase the comfort of the patient.
It would also be desirable to provide a lancer that has a mechanism to reduce radial movements of the plunger and thereby increase patient comfort by reducing radial forces introduced by the lancet stylet when it is penetrating the patient's tissue.